Field of the Invention:
The present invention relates to a heat-resistant, highly expansible sheet material used for supporting a catalyst carrier for a converter of automobiles for purifying exhaust gases, and to a process for the preparation of the sheet material.
Description of the Prior Art:
It is disclosed in Japanese Utility Model Publication No. 20523/1973 that a resilient ceramic heat insulator, for example fiberfrax, is used between a housing and a catalyst element embedded in a cartridge of a catalyst for the treatment of exhaust gases. It is also disclosed in Japanese Patent Application Laid-open No. 59211/1973 that a castable refractory excellent in heat resistance and heat insulation can be interleaved and hardened between an outer shell and an inner shell, which forms a reaction chamber inside, of an exhaust gas-purifying device. The refractory, comprising an aggregate principally composed of vermiculite or other light-weight aggregate and a highly heat-resistant binder for binding the aggregate, is used in the form of a slurry, with the addition of water or an activator to the powdery refractory for improving its fluidity.
It is disclosed in U.S. Pat. No. 3,441,381 that a catalytic apparatus having a cylindrical catalyst, the external diameter of which is smaller than the internal diameter of the casing, and a flexible resilient material provided under compression between the casing and the catalyst to tightly support the catalyst in the cylindrical casing is used for purifying exhaust gases. The flexible resilient material is a corrugated metal structure comprising metallic gauzes, which has many small holes.
It is disclosed in U.S. Pat. No, 3,916,057 that a heat-expansible sheet material, which shows such resilience that it can endure prolonged and repeated mechanical or thermal shock, comprising from 30 to 85% by weight of unexpanded mica, 60% by weight or less of an inorganic fibrous material, and from 10 to 70% by weight of an inorganic binder, is interleaved between the inner wall of a metallic container and a ceramic structure, in the process of mounting the ceramic structure in the metallic container.
It is also disclosed in U.K. Patent No. 1,023,425 that a heat-resistant and heat-insulating composition comprising a finely divided refractory material having a low density, for example a thingage vermiculite fibrous refractory such as asbestos, slag wool or glass fiber, artificial inorganic fiber, and a sodium silicate binder is used.
However, the above-mentioned heat-insulating material used in the cartridge disclosed in Japanese Utility Model Publication No. 20523/1973, which is in the form of a sheet principally composed of inorganic fiber, has a disadvantage of forming a gap between the housing and the catalytic element because of the deterioration in the strength of the sheet due to external stress such as vibration. The exhaust gas purifying device disclosed in Japanese Patent Laid-open No. 59211/1973 is also disadvantageous in that the highly heat-resistant and heat-insulating castable refractory used in the device loses its resilience once it is exposed to high temperatures, thus forming a gap between the outer shell and the inner shell, through which exhaust gases may pass. The resilient material made of metal disclosed in U.S. Pat. No. 3,441,381 is disadvantageous in that the metal material is gradually deteriorated in resilience and has a large thermal conductivity. The temperature of the device itself is raised due to the high thermal conductivity characteristic of the metal, which leads to the necessity of providing another heat-insulating layer outside and the complication of the structure. The sheet material disclosed in U.S. Pat. No. 3,916,057 is disadvantageous not only in poor expansibility at low temperatures due to the large amount of the binder but also in less satisfactory resilience and flexibility at high temperatures. The gasket material disclosed in U.K. Patent No. 1,023,425 is disadvantageous in the difficulty of being rolled around the catalyst carrier due to the poor flexibility of the material.